This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This program aims to determine the structures of proteins involved in cell membrane targeting, adhesion and signaling processes, in order to establish the mechanism and specificity of their interactions. There are three principal areas under investigation, all of which with crystals that require synchrotron radiation. 1. Cell-surface carbohydrate recognition in the immune system, focusing on serum Mannose-binding Proteins and how they trigger complement-mediated cell lysis, and DC-SIGN, an adhesion molecule that mediates activation of T cells by antigen-presenting cells, and which also serves to capture HIV and deliver it to T cells. 2. Architecture and assembly of intercellular junctions, studying the interactions of the proteins that link cadherin cell adhesion molecules to the cytoskeleton. The adherens junction protein beta-catenin is also an essential component of the Wnt signaling pathway, and its interactions with other Wnt pathway components are also being studied. 3. Proteins responsible for specific docking and fusion of intracellular vesicles with target membranes.